The long term evolution-advanced (LTE-A) Rel-10/11 technology of the 3rd generation partnership project (3GPP) is the enhanced LTE Rel-8 technology, which has a higher requirement on bandwidth than the LTE system and supports a peak data rate up to 1G. In order to meet the requirement for the bandwidth, the technique of component aggregation (CA) is adopted in the LTE-A system for expanding the bandwidth of the system. Moreover, various technologies of enhanced multiple-input multiple-output (MIMO) and the self-adaptive technologies are adopted in the LTE-A system to improve the data rate and the system performance.
In the above case, user equipment (UE) can support up to five component carriers. Generally, uplink channels in the LTE system include a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), a sounding reference signal (SRS) and a physical random access channel (PRACH). The channels may often be transmitted simultaneously. Therefore, the transmit power of the UE is prone to exceed the maximum transmit power of the UE, leading to power limitation, or the transmit power of the UE is prone to reach the interference level, leading to interference limitation. The following solutions are proposed for several different cases of the above problem.
1. PUCCH and PUSCH are transmitted simultaneously. The PUCCH can only be transmitted with a primary uplink carrier and the PUSCH can only be transmitted with a secondary uplink carrier. Therefore, in the case where the PUCCH and the PUSCH are transmitted simultaneously, a power zoom mechanism may be used. According to the power zoom mechanism, in the LTE-A Rel-10 system, the PUCCH is defined to have the highest priority, the PUSCH carrying uplink control information (UCI) is defined to have the middle priority and the PUSCH carrying only data is defined to have the lowest priority. In accordance with the above-mentioned order of priority, if there is still some power remained in the case where the transmit power for the channel with a highest priority is ensured, the remained power may be assigned to a channel with a second highest priority. Moreover, if the priorities for all the channels are the same, the transmit power for all the channels are decreased to scale and then the maximum transmit power are shared equally by all the channels
2. SRS and PUCCH are transmitted simultaneously. If a shortened PUCCH format is used in the PUCCH, the SRS is transmitted in the last symbol of the sub-frame (in the case where the sub-frame includes 14 symbols of normal cyclic prefix (NCP) or 12 symbols of extended cyclic prefix (ECP)). If the shortened PUCCH format is not used in the PUCCH, the SRS is discarded.
3. SRS and PUSCH are transmitted simultaneously. If the SRS and the PUSCH are transmitted with the same carrier, rate matching is performed on the PUSCH in accordance with 13 symbols (NCP) or 11 symbols (ECP) to empty out the last symbol to transmit the SRS. If the SRS and the PUSCH are transmitted with different carriers, the SRS is discarded.
4. PRACH and the above-mentioned channels are transmitted simultaneously. In the LTE-A Rel-10 system, it is impossible to transmit PRACH and other channel simultaneously, since the UE can only support the PRACH in a primary cell where the primary carrier locates. However, in the LTE-A Rel-11 system, different carriers are allowed to have different timing advance (TA) values and are classified into different timing advance groups (TAGs) according to the TA values, with the TA values of the carriers in each TAG being the same. The TA value of a TAG including a primary cell (PCell) takes the TA value of the PCell as reference. A TAG including only the secondary cells (SCells) may take the TA value of one of the SCells as reference. To obtain the TA value in the SCell, the system allows the PRACH to be existed in the SCell, for transmitting the RACH preamble to the UE. In the above case, there may be a problem that the PRACH in the SCell may be transmitted simultaneously in a same sub-frame with the PUCCH, the PUSCH and the SRS in the PCell or the PUSCH and SRS in other SCell. As shown in FIG. 1, in this case, the transmit power of the UE may exceed the maximum transmit power of the UE, leading to power limitation, or the transmit power of the UE may reach the interference level, leading to interference limitation.